I find it very easy to lock myself into one or two different ratios simply because I don't want to do math first thing in the morning. But sometimes, especially if there's coffee that's just finicky, a big swing in ratio can be just the thing.

My most commonly used ratio is 1:18, but I have a coffee (medium-light, washed) currently that I've mostly enjoyed iced and not hot. So I was going to try doing it hot with bypass this morning, but after tasting it at 1:10, it was really good, so problem solved I guess.